From 9dd51c94844bc7e5f8b1552511d31ed2c9bac05c Mon Sep 17 00:00:00 2001
From: Mike Buland <eichlan@xagasoft.com>
Date: Thu, 21 Feb 2013 03:55:56 +0000
Subject: Added the Bu::ReadWriteMutex, which is super awesome.  Also made the
 Bu::RandomBase::rand functions visible in the Bu::RandomCmwc class.

---
 src/unstable/readwritemutex.h | 75 +++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 75 insertions(+)
 create mode 100644 src/unstable/readwritemutex.h

(limited to 'src/unstable/readwritemutex.h')

diff --git a/src/unstable/readwritemutex.h b/src/unstable/readwritemutex.h
new file mode 100644
index 0000000..9e07047
--- /dev/null
+++ b/src/unstable/readwritemutex.h
@@ -0,0 +1,75 @@
+#ifndef BU_READ_WRITE_MUTEX_H
+#define BU_READ_WRITE_MUTEX_H
+
+#include "bu/mutex.h"
+#include "bu/condition.h"
+
+namespace Bu
+{
+    /**
+     * Mutex designed for situations where overlapped reading is safe, but
+     * overlapped writing isn't.  There are many, many good examples of this
+     * including most data structures, streams, etc. etc.
+     *
+     * Use this just like a normal mutex except that you use the
+     * lockRead/unlockRead and lockWrite/unlockWrite functions depending on
+     * weather the section of code your locking is reading data or changing
+     * data.
+     *
+     * This particular mutex is designed so that while a read operation is
+     * happening other read operations can also happen, but no write operations
+     * can occur.  While a write is happening, no other write or read operation
+     * can continue.  There is an extra feature to ensure writes get a chance
+     * to complete, when a lockWrite is issued, all current read operations
+     * continue, but future read operations block until the write is complete.
+     */
+    class ReadWriteMutex
+    {
+    public:
+        ReadWriteMutex();
+        virtual ~ReadWriteMutex();
+
+        /**
+         * Lock the mutex for reading.  Multiple code sections can hold a read
+         * lock at the same time, but write locks will wait for all read locks
+         * to be released before continuing.  Read locks will also wait if
+         * there is an active write lock.
+         *
+         * It is very important to not make any changes to your data within
+         * a read lock.
+         */
+        void lockRead();
+
+        /**
+         * Release a read lock.
+         */
+        void unlockRead();
+
+        /**
+         * Lock the mutex for writing.  Only one code section can have a write
+         * lock at any given time.  No code sections can be in a locked read
+         * section while a write lock is held.  When a write lock is requested
+         * all following read locks will block until the write operation is
+         * started, ensuring writes always get a chance to execute.
+         *
+         * Within a write locked code section feel free to change your data
+         * and read your data.  It is imparative to spend as little time as
+         * possible in a write-locked section.
+         */
+        void lockWrite();
+
+        /**
+         * Release a write lock.
+         */
+        void unlockWrite();
+
+    private:
+        Bu::Mutex mRead;
+        int iCounter;
+        Bu::Mutex mWrite;
+        Bu::Condition cWrite;
+        bool bWantWrite;
+    };
+};
+
+#endif
-- 
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